doc: add for errors

src/error.rs

@@ -1,14 +1,26 @@
 use std::error;
 use std::fmt;
 
+/// A helper type for any result with persistence error.
+///
+/// Use this type in your repository or in something else that implements methods for your persistence.
 pub type Result<T> = std::result::Result<T, PersistenceError>;
 
+/// All supported kinds of persistence error
 #[derive(Debug)]
 pub enum PersistenceError {
+    /// Returns if we cannot get a connection from pool.
     GetConnection,
+    /// Returns if we cannot upgrade connection to transaction.
+    #[cfg(feature = "nightly")]
     UpgradeToTransaction,
+    /// Returns if we cannot commit transaction.
+    #[cfg(feature = "nightly")]
     CommitTransaction,
+    /// Returns if we cannot rolls back transaction.
+    #[cfg(feature = "nightly")]
     RollbackTransaction,
+    /// Rest database errors contains here.
     DbError(Box<dyn std::error::Error>),
 }
 
@@ -16,11 +28,16 @@ impl fmt::Display for PersistenceError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             PersistenceError::GetConnection => f.write_str("Cannot get connection"),
+            #[cfg(feature = "nightly")]
             PersistenceError::UpgradeToTransaction => {
                 f.write_str("Cannot upgrade connection to transaction")
             }
-            PersistenceError::CommitTransaction => f.write_str("Cannot commit transaction"),
-            PersistenceError::RollbackTransaction => f.write_str("Cannot rollback transaction"),
+            #[cfg(feature = "nightly")]
+            PersistenceError::CommitTransaction => {
+                f.write_str("Cannot commit changes of transaction")
+            }
+            #[cfg(feature = "nightly")]
+            PersistenceError::RollbackTransaction => f.write_str("Cannot rolls transaction back"),
             PersistenceError::DbError(err) => write!(f, "DbError: {}", err),
         }
     }